Abstract:

Purpose: Stereotactic radiation therapy and stereotactic radiosurgery deliver radiation precisely to tumors, using special equipment to position and demobilize patients. The VisionRT system, with its component AlignRT, is a non-invasive stereotactic positioning and tracking system that uses cameras to capture infra-red images of patients, and process these images, to obtain precise shifts in patient location. This thesis evaluates the accuracy of the AlignRT system accuracy while setting up and tracking patients.
Methods: This thesis investigates the setup accuracy of the AlignRT system based on the CT contour of an anthropomorphic phantom exported to the AlignRT from treatment planning systems, and compared results to those provided by the X-ray image-based positioning system ExacTrac. Measurements utilize a modified Winston-Lutz technique to derive the deviation of the planned isocenter relative to the radiation isocenter. A phantom embedded with a 16 mm metallic sphere and a Winston-Luts pointer were used as the positioning objects. A Varian electronic portal imaging device were utilized to obtain images. A Vidar scanner and RIT113v5.2 software were used to process images obtained in Winston-Lutz tests. Based on the equations derived for Winston-Lutz tests, shifts of the planned isocenter relative to the radiation isocenter were calculated, which were then used to judge the positioning the objects. Both positioning and tracking modes of AlignRT were tested. AlignRT, ExacTrac, and Winston-Lutz test measurements were all performed on the same Varian Novalis Tx system.
Results: The results indicated that the AlignRT gave a positioning error of more than 1 mm based on CT contours and at small couch angles, which was larger than the clinical tolerance of 1mm for stereotactic radiation therapy. The positioning error would be less if the AlignRT system could be recalibrated with the same isocenter as the X-ray system or utilize its own initial image instead of CT contour. At larger couch angles, the positioning errors were larger than 1 mm even after recalibration. A further investigation and collaboration with the manufacture would be required to obtain desired accuracy.